1. Field of the Invention
The present invention relates to a liquid crystal display device and to a method for driving the same and more particularly to the liquid crystal display device and the method the same that can be suitably used in a device such as a liquid crystal projector in which a screen of high quality with flicker being reduced is required.
The present application claims priority of Japanese Patent Application No. 2002-172039 filed on Jun. 12, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
A conventional liquid crystal display device, in order to prevent deterioration of a liquid crystal material, is driven with an alternating current so that a polarity of a voltage to be applied to the liquid crystal material is alternately reversed at predetermined time intervals.
The conventional liquid crystal display device of this type, as shown in FIG. 11 for example, includes a liquid crystal panel 10, a liquid crystal driving circuit 20, and a common voltage generating circuit 30. The liquid crystal panel 10, as shown in FIG. 12, has a plurality of signal lines X1, X2, . . . , Xn to which a corresponding pixel data signal D is fed, a plurality of scanning lines Y1, Y2, . . . , Ym to which a scanning signal V is fed, a plurality of MOSFETs (Metal Oxide Semiconductor Effect Field Transistors) 11ij (i=1, 2, . . . , n; j=1, 2, . . . , m) each being placed at a point of intersection of each of the signal lines X1, X2, . . . , Xn and each of the scanning lines Y1, Y2, . . . , Ym pixels (picture elements) 12ij (i=1, 2, . . . , n; j=1, 2, . . . , m), capacitors 13ij (i=1, 2, . . . , n; j=1, 2, . . . , m), “Cs” line being commonly connected to each of the capacitors 13ij, and a common electrode 14 being connected commonly to each of the pixels 12ij and to which a common voltage Vcom (FIG. 11) is applied, in which an image is displayed by a pixel data signal D fed to the pixels 12ij on the scanning lines Y1, Y2, . . . , Ym to be selected by the scanning signal V.
The liquid driving circuit 20 reverses a polarity of a pixel data signal D corresponding to a video signal “in” relative to a reference voltage Vf for every one horizontal period and feeds the reversed signal to each of the signal lines X1, X2, . . . , Xn in the liquid crystal panel 10 and, at a same time, feeds the scanning signal V in predetermined order to each of the scanning lines Y1, Y2, . . . , Ym The common voltage generating circuit 30 generates the common voltage Vcom.
In the conventional liquid crystal display device, as shown in FIG. 13, to the liquid crystal panel 10 is applied the common voltage Vcom having a predetermined voltage level and to the liquid crystal driving circuit 20 is applied the reference voltage Vf having a predetermined voltage level and an image corresponding to the pixel data signal D is displayed. The pixel data signal D is reversed relative to the reference voltage Vf for every one horizontal period. Moreover, the common voltage Vcom is adjusted so that flicker occurring due to the reversal of the pixel data signal D can be minimized.
However, the conventional liquid crystal device as described above has following problems. That is, in the conventional technology, in order to minimize flicker, only the common voltage Vcom is calibrated. However, since the common electrode 14 is placed over all areas of the liquid crystal panel 10, due to a voltage drop caused by a resistor component of the common electrode 14, in many cases, the common voltage Vcom is not made uniform over all areas in the liquid crystal panel 10. For this reason, the common voltage Vcom to be used to minimize flicker varies in the liquid crystal panel 10 and, as a result, it is impossible, in some cases, to successfully perform calibration to minimize flicker over all areas of the liquid crystal panel 10. For example, since the common voltage Vcom to be used when flicker occurring in side regions in the liquid crystal panel 10 is minimized is made different from the common voltage Vcom to be used when flicker occurring in regions in a vicinity of a center of the liquid crystal panel 10 is minimized, a phenomenon occurs in which the common voltage Vcom to be used when flicker is minimized over all areas of the liquid crystal panel 10 can not be successfully calibrated. Therefore, a problem arises that display image quality is degraded.
To solve this problem, a liquid crystal device is disclosed in Japanese Patent Application Laid-open No. 2000-305063. The disclosed liquid crystal device is so constructed that a common voltage can be fed from each of the right and left sides in order to enable optimum calibration of flicker at both right and left sides within a face of a liquid crystal panel. It is expected by using this configuration that an optimum common voltage is applied at both the left and right sides of the liquid crystal panel and flicker occurring within the face of the liquid crystal panel is made almost uniform; however, to achieve such the effect, it is necessary to construct the liquid crystal panel so as to have special configurations, which are not readily achieved. Moreover, since a required optimum common voltage is different between portions on both sides of the liquid crystal panel and its central portions, it is difficult to successfully reduce flicker within the face of the liquid crystal panel. When the liquid crystal panel is increased in size in particular, such a tendency becomes remarkable.